Presently, large plastic bottles (e.g., 32 ounce, 64 ounce, 128 ounce, etc.) with handles for lifting, carrying and pouring generally are made by the extrusion blow molding process.
Initially an extruder forms large diameter preforms, hollow tubes known as parisons, and the parisons are positioned within blow molds having the desired final shape of the bottles. In each blow mold a portion of the parison is pinched off to form a handle shape and the pinched parison is blown to its final bottle dimensions with a hollow handle and an interconnecting web. Thereafter, the web is removed to provide a handle for gripping, lifting, carrying, and pouring.
In forming such hollow handles relatively high plastictemperatures and substantial parison thicknesses are required to provide satisfactory fusion in the pinched and blown parison. Also, the parison must have a large enough diameter so that it will essentially traverse the breadth of the bottle when pinched and blown.
The procedures for forming these bottles are well known. See Modern Plastics Encyclopedia, Vol. 54, No. 10A, 1977-1978, McGraw-Hill Publishing Co. (e.g., section on "Blow Molding" at page 230, et seq.; also see section on "Injection Blow Molding" at page 232 et seq.).
Depending on the design, the pinched, blown hollow handle can provide ease in carrying, lifting and pouring, or simply ease in carrying and lifting. In the instance of a pouring handle, moreover, the need to grip the side walls of the container is eliminated. This can result in lighter weight bottles at lower costs. These and other features make the pouring handle very popular for large plastic bottles made from a wide variety of thermoplastic materials including polyolefins (polyethylene and polypropylene) and polyvinyl chloride.
However, these methods and the resulting bottles with hollow handles do have drawbacks. For example, decreasing the amount of plastic, used to form the bottles, known as "light weighting", is limited in many cases by the need for adequate parison thickness to provide the requisite fusion along the extensive pinched off areas.
Another limitation is that the required large diameter parison produces bottles having wide variations in wall thicknesses, especially at and near the sidewall at the bottom juncture and at the shoulder area - the most vulnerable areas to drop impact and denting forces. This results because the pinch off distributes the parison into thick areas at each end of the pinch off and in very thin areas in the blown bottle at right angles to it.
Further, hollow handles generally are precluded from use in refillable containers, such as may be found in dairy uses. Cleaning and rinsing the interior of such handles is virtually impossible.
Still another limitation is that the relatively high fusion temperatures required to form the pinched off hollow handles cannot be used to form handles in the newer stretch blow molding process for forming plastic bottles. This process differs from the hollow handle blow molding process in that the parison is first stretched and then blown while at temperatures which are much lower than the fusion temperatures, typically within the 100.degree. F. range above T.sub.g (the temperature at which the plastic material passes from the glass phase to the rubber phase). This procedure, which is known as stretch blow molding, or orientation blow molding, is not only replacing earlier blow molding techniques, but is opening up new markets. Advantages of the new procedures are related to the biaxial orientation of the polymeric material. While the parison is at a temperature insufficient to permit free plastic flow it is expanded biaxially to conform with the blow mold. The temperature of operation typically within the 100.degree. F. range immediately above T.sub.g is such that expansion introduces true strain into the material, and this strain is translated into a definable polymer orientation which results in a number of attributes.
Alignment of polymer molecules results in increased tensile strength, as well as increased clarity, increased impact strength, and reduced creep. A vast market for carbonated soft drink containers is a direct result of significantly improved gas barrier properties.
Suitable container materials for stretch-blow molding are substituted and unsubstituted thermoplastic hydrocarbons. Commonly used materials at this time include acrylonitrile, polyvinyl chloride, polyethylene terepthalate, and polypropylene. This newer procedure also is known. See Modern Plastics Encyclopedia, Vol. 54, No. 10A, 1977-1978, McGraw-Hill Publishing Co. (e.g., section on "Stretch-Blow Molding" at page 233 et seq.).
The problem with producing plastic containers with handles using the stretch blow processes results from the nature of the process and condition of the plastic at the time it is biaxially oriented. It is not possible to produce handles by the aforementioned parison pinch-off technique because the plastic temperature required for suitable molecular orientation is much too low to permit adequate fusion of the plastic. To initially form the handle at elevated temperatures and then to cool to biorientation temperatures before stretching and blowing would yield handles, and substantial other unoriented portions of the container, with inferior containment and other properties.